Histone deacetylases (HDACs) catalyze the removal of acetyl groups from histones, proteins that organize and modulate the structure of chromatin in nucleosomes. HDAC-mediated deacetylation of chromatin-bound histones regulates the expression of a variety of genes throughout the genome. Importantly, HDACs have been linked to cancer. To date, eleven major HDAC isoforms have been described (HDACs 1-11). Certain HDACs are overexpressed in, e.g., prostate cancer (HDAC1), colon cancers (HDAC3), and breast cancers (HDAC6). Indeed, HDAC activity is increasingly recognized as playing an important role in the onset and progression of cancer, as well as other health conditions.